- 學位論文
應用非線性有限元素法於Dynesys與Cosmic混合式腰椎固定器之特性研究
Nonlinear Finite Element Study on Biomechanical Characteristics of Dynesys and Cosmic Lumbar Hybrid Fixation
摘要
在臨床上有許多不同型態的植入物被用於治療各種腰椎病變，較早使用之骨融合手術雖然可以限制手術固定節的運動自由度，但確會使手術區鄰近節產生加速退化之問題。因此使用動靜態混合固定器之非骨融合手術治療方式逐漸受到重視，也促成不同形式動態椎弓足固定器的崛起，本研究中的Dynesys與Cosmic動態固定器即為其中兩種。本研究以一完整的腰椎有限元素分析平台，針對臨床上常用的Dynesys與Cosmic動態固定器作生物力學上之特性比較，並探討兩種動態固定器的負載轉移機制與對鄰近節產生的加速退化問題。研究結果發現，這兩種動態固定器對於過度節在可動性上都有著保留運動能力和保護負載的效果，但也造成鄰近節的加速退化。相較於Cosmic系統，Dynesys系統於過度節保有較高的可動性。因此Cosmic系統適合較嚴重退化的過度節使用，而Dynesy系統則推薦使用於退化初期之過度節椎間盤。同時在Cosmic系統中骨頭-螺絲交界面有較高的應力分布，容易造成骨螺絲鬆脫、滑脫或是斷裂。本研究更進一步探討Dynesys動態固定器中撓性連接桿預緊力對於椎骨組織反應與螺絲-套筒行為的影響，以提供關於Dynesys螺絲-墊片關節的運動保留與負載保護機制的詳細訊息。研究結果也發現Dynesys系統中增加預緊力對於鄰近節的影響並不大，但卻顯著影響螺絲-套筒間的受力與骨頭-螺絲間的應力。
並列摘要
Clinically there are many different types of implants used to treat a variety of lumbosacral diseases. Although the lumbosacral fusion surgery with static fixators can limit the mobility and provide immediate stability of the fixed segments. However, it might cause the junctional problem of surgical treatment and accelerate the degeneration of adjacent segments. As an alternative, some dynamic fixators have been developed to limit both kinematic and mechanical constraints on the fixed segments, thus reducing the occurrence of the junctional problem. The Dynesys and Cosmic system in this study are the two major types of dynamic fixators. A complete finite-element model of five-segment lumbroscral column was used to compare the biomechanical characteristics of Dynesys and Cosmic lumbar hybrid fixation. This study investigated the load-transferring mechanisms of these two dynamic fixators and the fixator- induced effects on the junctional problem of the adjacent segments. Both systems show the ability to protect the transition segment but deteriorate the adjacent segments. The screw-hinge joint and the stiffer rod of the Cosmic system signifi cantly constrained the motion pattern of the transition segment. Comparatively, the Dynesys screw-spacer interfaces make contact with and depart from each other during motion; thus providing higher mobility to the transition segment. However, the highly stressed distribution at the Cosmic bone-screw causes the screw and hinge prone to pullout and fatigue failures. Moreover, the pretension of the Dynesys cord was varied to evaluate its effects on both tissue response and screw-spacer behaviors by the same finite-element model. This study aimed to provide detailed information about the motion-preserving and load- shielding mechanisms of Dynesys screw-spacer joint. In the results, author found that the cord pretension has a minor effect on the adjacent segments in comparison with the transition segment. However, the stress at the screw hub and force of the screw-spacer contact of the 300 N pretension were significantly higher than without pretension.